Barriers and bridges for sustaining functional habitat networks: A macroecological system analysis of wet grassland landscapes

Abstract This study aims at supporting the maintenance of representative functional habitat networks as green infrastructure for biodiversity conservation through transdisciplinary macroecological analyses of wet grassland landscapes and their stewardship systems. We chose ten north European wet grassland case study landscapes from Iceland and the Netherlands in the west to Lithuania and Belarus in the east. We combine expert experiences for 20–30 years, comparative studies made 2011–2017, and longitudinal analyses spanning >70 years. Wader, or shorebird, (Charadrii) assemblages were chosen as a focal species group. We used evidence‐based knowledge and practical experience generated in three steps. (1) Experts from 8 wet grassland landscapes in northern Europe's west and east mapped factors linked to patterns and processes, and management and governance, in social‐ecological systems that affect states and trends of wet grasslands as green infrastructures for wader birds. (2) To understand wader conservation problems and their dynamic in wet grassland landscapes, and to identify key issues for successful conservation, we applied group modeling using causal loop diagram mapping. (3) Validation was made using the historic development in two additional wet grassland landscapes. Wader conservation was dependent on ten dynamically interacting ecological and social system factors as leverage points for management. Re‐wetting and grazing were common drivers for the ecological and social system, and long‐term economic support for securing farmers’ interest in wader bird conservation. Financial public incentives at higher levels of governance of wetland management are needed to stimulate private income loops. Systems analysis based on contrasting landscape case studies in space and over time can support (1) understanding of complex interactions in social‐ecological systems, (2) collaborative learning in individual wet grassland landscapes, and (3) formulation of priorities for conservation, management, and restoration.


| INTRODUC TI ON
Research into broad-scale general patterns and trends of ecological systems, the processes that underlie them, and relationships with governance, planning, and management in social systems, has long called for new modes of knowledge production and learning (Brown, 1995;Gibbons et al., 1994). Systems analyses (Maani & Cavana, 2000) defining both shallow and deep leverage points for sustaining ecological systems is an effective approach (Meadows, 2008).
Ultimately, a resilient ecosphere is a foundation for landscapes' social and economic systems (United Nations, 2015). Maintaining the integrity of intact ecosystems with representative and functional habitat networks supporting biodiversity conservation and human well-being is thus a key component of proactive global and national environmental strategies (Watson et al., 2018). Policies and terms like ecological networks and greenways (Jongman et al., 2004(Jongman et al., , 2011, ecological infrastructure (Angelstam, Barnes, et al., 2017), and green infrastructure (European Commission, 2013) capture this key component. Nevertheless, a traditional focus on protected areas and species and not functional habitat networks prevails (Harvey et al., 2017). Thus, habitat alteration, fragmentation, and loss continue, which results in reduced functionality of habitat networks Beyer et al., 2020;Correa Ayram et al., 2016).
According to Grint (2008), decision-makers have three types of problems: tame, critical, and wicked. While for the first two, being less or more urgent to handle, there are common well-established best practices that can be scaled up. In contrast, for wicked problems, there is no consensus of the problem, and there is disagreement among actors and stakeholders, including researchers with different lenses (Maxwell et al., 2020). Nikolakis and Innes (2020:13) listed three components for tackling wicked problems: collaborative governance, adaptive leadership, and holistic system-based thinking.
Comparative studies of multiple landscapes as social-ecological systems are effective for holistic systems analyses about the green infrastructures Dawson et al., 2017Dawson et al., , 2021.
Already Von Thünen (1910) observed that the types and intensities of land use were related to the distance from the market. The European continent is a prime example of a region with a diverse history of land use and management. Loss of habitats in Europe is related to a generally expanding human footprint in terms of increasingly intensified land use from the core to the periphery of economic development (Bobiec et al., 2019;Gunst, 1989;IPBES, 2019).
This takes place in spite of considerable resources being spent on nature conservation through the creation of protected areas (Kati et al., 2015), "re-wilding" (Perino et al., 2019), and habitat/landscape restoration (Emanuelsson, 2009) with the aim to maintain functional habitat networks. Europe thus has distinct gradients of alteration, fragmentation, and loss of remnants of both traditionally multifunctional cultural landscapes and naturally dynamic forest landscapes (Angelstam, Khaulyak, et al., 2017;Angelstam, Naumov, et al., 2018Edman et al., 2011;Manton et al., 2019;Puumalainen et al., 2003). Intensification of land management in European centres of economic growth is thus responsible for declines and even local extinction of species (Storkey et al., 2012;Thorup, 2006) and modification of trophic interactions Manton et al., 2019). In comparison, land management and use in European peripheries have developed slower, are generally less intensive, and have better retained ecological patterns and processes in landscapes McDonnell et al., 2008;Valasiuk et al., 2018).
Transformation of naturally dynamic ecosystems into anthropogenic land covers has both negative and positive consequences for ecosystem processes, habitats, and species in Europe Price, 2003). Transitioning natural forest ecosystems by management to produce industrial raw material generally leads to loss of biodiversity . In contrast, the emergence of agriculture based on animal husbandry often created cultural landscapes with large areas of high conservation value farming areas, such as wet grasslands and other naturally open landscapes with grasslands and heaths used for haymaking and as pastures for grazing (Emanuelsson, 2009;Eriksson & Cousins, 2014;Hejcman et al., 2013;. To benefit from the high nutrient content of soils, wet grasslands were thus expanding in river deltas, along seashores, in flooded areas along rivers and streams, or through man-made seepage areas (Emanuelsson & Möller, 1990). However, driven by the agricultural and industrial revolutions over the last century, large differences among European agricultural landscapes have developed. Thus, countries outside the EU, like some former parts of the USSR in the eastern periphery of Europe have retained traditional practices (Valasiuk et al., 2018).
Iceland in the northern periphery has developed its own agricultural policies and even encouraged the expansion of animal husbandry through expanded grassland areas (Fridriksson, 1972;Helgadóttir et al., 2013). This has resulted in considerable variation in the state and trends of wet grassland vegetation patterns, such as patch size and spatial configuration, and processes, such as re-wetting, grazing, mowing, and predation in cultural landscapes in Europe Manton et al., 2016Manton et al., , 2019Smart et al., 2006), and the associated population trends of waders, or shorebirds (Charadrii) (Thorup, 2006;Verkuil, Karlionova, et al., 2012;).
Noting the limited success of traditional conservation management based on protected areas and species only, Harvey et al. (2017) stressed the need for integrative approaches focusing on ecological networks as a conservation target. In particular, this would allow

T A X O N O M Y C L A S S I F I C A T I O N
Applied ecology for better conceptual bridging of ecosystem-level supporting processes and emerging services. With annual global scale migration routes spanning multiple continents (Verkuil, Karlionova, et al., 2012;van Vliet et al., 2015), waders are excellent model organisms, often used as indicators of ecosystem health (Sutherland et al., 2012). To address the threats faced by deteriorating semi-natural grasslands in breeding areas, knowledge production and learning should also pay more attention to the inherent socialecological complexity of them (Herzon et al., 2021). The dynamic cultural wet grasslands were well suited for wader birds, at different points in time depending on the land use, due to a range of factors like abundant food, favorable hydrological regimes, grass mowing for fodder, grazing, and livestock churning the soil (Emanuelsson, 2009;Laidlaw et al., 2015;Leito et al., 2014). Regional differences in the timing of cultural wet grassland expansion and decline have thus led to frontiers of emergence and degradation of wet grassland landscapes, and very few wader populations have remained viable or shown increases (Gunnarsson et al., 2005;Johannesdottir et al., 2019). The sequence of rise and fall of grasslands is paralleled by the pattern that some European regions exhibit declines in breeding migratory waders (Gill et al., 2007;Schekkerman et al., 2009). Waders have an umbrella species function: management for threatened waders has a strong supporting impact on meadow plants and amphibians (Rannap et al., 2017). In Europe, the ruff (Philomacus pugnax) and black-tailed godwit (Limosa limosa) function as flagship species (Schlagloth et al., 2018) for wader bird communities in wet grasslands (Van der Vliet, 2015). Optimal breeding habitat for ruff and black-tailed godwit is thus often a suitable breeding habitat for other waders, such as dunlin (Calidris alpina), redshank (Tringa totanus), and lapwing (Vanellus vanellus).
The aim of this study is to analyze the dynamics of multiple wader landscapes as social-ecological systems that determine the distribution and abundance of wader populations that depend on wet grasslands as a functional green infrastructure. Using a transdisciplinary approach, researchers and practitioners collaborated to understand how different drivers of wader bird distribution and abundance are interlinked. We integrate macroecological methods, comparative analyses by experts, meta-analyses, peer-review publications, combined with a multiple landscape case study approach based on reviewing the knowledge from a suite of wet grassland landscapes at different stages of development of green infrastructure functionality, system analysis using causal loop modeling, and validation using landscape history reviews. The discussion focuses on the need to address the complexity of wet grasslands as socialecological systems for biodiversity conservation and human wellbeing, and how systems analysis can contribute.

| Multiple landscapes as case studies
Research aimed at studying relationships among different variables, which explain an outcome variable, should be based on data collection representing contexts with sufficient variation of parameter F I G U R E 1 Methodological approach F I G U R E 2 Wet grassland case study landscapes in northern Europe. Dark gray boxes with white text represent contemporary case studies used for causal loop modeling with both researchers and practitioners. Light gray boxes with black text represent wet grassland landscapes of the past are used for validation values in the variables of interest (Yin, 2014). However, the design of dose-response studies can determine the conclusions (Angelstam, Pedersen, et al., 2018). Studies of factors affecting habitat network functionality therefore require study areas that mirror both sufficient spatial extents and different levels of land-use intensification.
This calls for a macroecological approach (Brown, 1995), which relies on multiple landscapes as case studies in the regional gradient of landscape history . Therefore, the regional diversity of landscapes and regions on the European continent provides unique opportunities to develop evidence-based knowledge for biodiversity conservation. Noting the issue that social-ecological research is composed mainly of consolidated groups of scientists from developed countries leading work of peripheral barely consolidated groups (Santiz et al., 2021) this study includes a geographically and thematically broad portfolio of co-authors.
Following the terminology of Stake (2003), each landscape unit of study is a "bounded" separate entity in terms of place and space with physical boundaries hosting a neighborhood, and planning and management organizations, or histories. With a single case study approach, one can do in-depth exploration of a specific bounded system. Based on several different cases as a "collective case design" (Figures 1 and 2), with several instrumental bounded cases, we aimed at gaining in-depth understanding of the opportunities and barriers for GI maintenance; much more than any single case can provide (Chmiliar, 2010;Yin, 2014).
Focusing on the variation among contemporary landscapes in northern Europe's west and east we selected 8 case study areas (Appendix S1), which represent temporal changes in wet grasslands and wader population trajectories over the past 20-30 years. Additionally, the status of two wet grassland landscapes 70-200 years ago was used for validation (Appendix S2); (see wet grassland patches (Rannap et al., 2017), and the presence and trends of different wader species (see  and the proportion of the regional species pool. Based on this we created a ladder of predicted relative wader population sustainability ( Figure 3). Using the idea of Europe as a "time machine" and a laboratory for learning (Angelstam et al., 2011), the choice of case study landscapes thus followed the recommendation of information-oriented selection with critical cases (Flyvbjerg, 2006). This approach maximizes information from a small number of cases, and these are selected due to their information content and for their generalization characteristics.

| Mapping of drivers, systems analysis, and validation
To support a systems perspective on landscapes as coupled human and nature systems, we chose the multi-tiered social-ecological system (SES) framework (Partelow, 2018). This is useful for diagnosing both social systems focusing on governance interactions at multiple levels and outcomes in ecological systems with a focus on their sustainability at multiple scales. The SES framework has evolved into a systematic approach to understand how different SESs can be sustained (McGinnis & Ostrom, 2014). We used a multi-method approach in three steps to understand the dynamics of wader populations in different social-ecological contexts.

F I G U R E 3
Illustration of the development of wet grassland case study landscapes ( Figure 2, see also  from natural via anthropogenic to degraded, followed by attempts towards restoration The first step was to gather researchers and practitioners working within the 8 selected wet grassland landscapes for a 3day workshop in December 2016 to synthesize expert knowledge (Pearce-Higgins et al., 2017). We collectively listed variables capturing drivers in social-ecological systems affecting waders in local wet grassland landscapes. The workshop participants were interviewed using a semi-structured method (Flick, 2006) focusing on drivers which determine the distribution and abundance of breeding waders and the grassland dynamics on the local site, and effects of management and government initiatives. The results from the interviews to extract experts' experience were complemented with supporting evidence from the literature (Appendix S1). As a framework to list variables as drivers in ecological systems we divided them into pattern and process (Turner, 1989) at local, landscape and regional scales. For social system drivers, we focused on governance and management at different levels.
Second, we used system dynamics and a group modeling approach (Hovman, 2014;Maani & Cavana, 2000;Sterman, 2000) collaboratively involving both nonacademic experts and researchers during the same workshop to develop conceptual models covering social, economic, and ecological aspects of wet grassland governance and management aimed at maintenance of a functional green infrastructure for wader bird populations. Applying a systems dynamics approach, the structures and nonlinearity of wet grasslands as complex socio-ecological systems can be analyzed and the cause-relationship, feedback loops, and leverage points identified. The group modeling method allows all the participants to jointly define the system and its boundaries (Reed, 2008). By using Causal Loop Diagrams (CLDs), the complex dynamic research question can be structured and simplified (Haraldsson & Sverdrup, 2004). This process means that the participants are directly involved in the modeling work and jointly develop and review their understanding of the wet grassland/wader system, and the drivers and feedback. In the causal loop diagrams, each causal link has a polarity (+) when the direction of effect of the dependent variable is the same as the independent variable, and (−) when the direction is the opposite. The polarity of each feedback loop is essential for understanding the system's behavioral directionality, resulting in the magnification of the original effect (a reinforcing loop) or an equilibrating response (a balancing loop) (Sterman, 2000). Using group modeling allows the individual insights to expand outside their experience fields, thus developing a joint systems-based understanding of the complex problem (Elbakidze et al., 2015;Rouwette et al., 2011).
At the start, the participants formulated the problem articulation through three social-ecological questions for the modeling sessions, (1) What determines the breeding success of waders? (2) How can optimal land management for waders be achieved? (3) How to generate community interest in wader conservation? The facilitator drew and adjusted the CLDs on a whiteboard following the participants' discussion about cause and effect, and critique and improvement. After the workshop, the CLDs were sent out to the participants for a final evaluation. This method, with continuous and collective peer-review, allows the understanding of the system under study by all participants, and to be presented unambiguously and transparently.
The modeling was guided by three assumptions. The first is that evidence-based knowledge about flagship waders such as the ruff and the black-tailed godwit (Thorup, 2006;Verkuil, Karlionova, et al., 2012; can be used to identify factors needed to sustain viable populations of waders on wet grasslands in general during the breeding season. The second assumption is that breeding success, and not adult survival during the nonbreeding season, is the key driving factor (Roodbergen et al., 2008). The third assumption is that no radical changes in pressures and threats at the wader winter area have been identified during the past 2-3 decades, which is the period that this study represents.
Third, we validated the results from the comparative analysis of eight case study landscapes through a comparison with the long-term history of two additional wet grassland landscapes (see Appendix S2).

| Key factors affecting wader bird populations
The group discussions on the case studies clearly showed that experts' experience was that wader bird population dynamics are dependent on both ecological and social system factors. The interview step identified ten key social-ecological system variables (or drivers) for sustainable wader bird breeding in the 8 case study landscapes (Table 1). Ecological factors included soil quality, habitat fragmentation, predation pressure, size of wet grassland, edge effects, water condition factors (water table), and social system drivers (human management through grazing, mowing, draining). The interview results clearly showed the interconnection among drivers, and the complexity of the social-ecological system, which was further analyzed during the group modeling.

Habitat patch quality
The key qualities were water table, plant community composition, and structure and soil quality ( Table 1). Availability of water and appropriate vegetation structure on different scales were described as key factors determining patch quality. This is in line with Leito et al. (2014) showing that wader abundance was most strongly related to water level as a key factor for breeding habitat quality both positively and negatively. For some wader species, shallow open ponds were important for breeding success. Ivask et al. (2007) found that the water table, and flooding events, regulates resource availability for waders. The wader food resources are also dependent on overall TA B L E 1 Presence (1) and absence (0) of ecological and social system variables as drivers identified for wader population dynamics sorted from local (top) to regional (bottom) across eight current case study areas soil quality, or nutrient-rich patches in the landscape. Soil quality regulates patch vegetation composition, structure, and plant growth capacity. Berg and Hiron (2012) identified a dynamic relationship between water table, soil quality, and hydrological regime controlling plant community composition and structure.

Patch diversity
Waders use several different vegetation types to fulfill their needs during breeding. A diverse landscape structure including different patch types is therefore a key driver for breeding success (Laidlaw et al., 2015). For example, while the habitat needs to be wet and open, a protective vegetation structure for the chicks is essential during the breeding period and nests of some species require concealment. A set of wet patches around optimal feeding patches may reduce predation as wet barriers tend to lower the searching efficiency of those predators using mainly smell as a cue, e.g., red fox (Vulpes vulpes).

Fragmentation and patch size
Large (≥100 ha) and wide (mean width ≥200 m) meadows were an overall positive factor for favorable wader breeding conditions (see also Rannap et al., 2017). An open area without woody vegetation providing perches decreases predation risk.
Due to changes in agricultural techniques and intensity over the last two centuries, the fragmentation of wet grasslands has increased. For example, Manton and Angelstam (2018) used historical maps and agricultural statistics to show how the wet grassland in the Kristianstad case has been continuously lost and fragmented. Combining fragmentation and patch size they estimated a 98% decline in semi-natural meadow habitat network functionality during the last two centuries. Emanuelsson (2009) showed how European cultural wetland landscapes have continuously been fragmented due to agricultural development and the decreased need for hay from natural meadows.

Water table fluctuation
This driver is closely linked to the habitat quality factor. Flooding increases the meadow nutrient condition, which improves hay production (Emanuelsson, 2009;. The timing of the water table fluctuation over the breeding season is important for wader breeding (Eglington et al., 2008). Too deep water in spring forces the returning waders to seek other breeding areas. Drained wetlands lack this variation. Widespread drainage of wetlands for intensive agriculture has led to a drastic decline in the area of speciesrich wet grassland and transformed species compositions .

Grazing
Grazing by livestock is a process to keep vegetation height at an optimal level over the breeding season, both for wader food supply and nest concealment. Historically, wet grasslands' provision of pastures and meadows was enhanced to satisfy the needs for animal husbandry for food and manure production. Wet grasslands were thus managed by grazing and mowing (see below). In the absence of grazing, shrubs and tall grass species encroach, and habitat suitability is reduced (Leito et al., 2014). Experiences from the Mälardalen case study (Berg et al., 2002) indicate that the timing of grazing in spring affect the breeding success of wader populations. However, both livestock used for grazing and overstocking may have a potential negative effect. For example, studies from Iceland show that sheep may eat wader eggs and horses can trample the nests when grazing (Katrínardóttir et al., 2015) and a study in Finland showed that trampling of dunlin nests had a significant negative effect on hatching success (Pakanen, 2011;Pakanen et al., 2011).

Predation
The factor of predation can be divided into predator abundance, the number of predator species, and the amount of nest predation (  Marzluff & Neatherlin, 2006). The variation in corvid abundance is also reflected in rates of artificial nest predation .
Climate change Smart and Gill (2003) listed a range of potential impacts of climate change on breeding waders. In this study change in winter temperature due to climate change was identified as a negative driver in the Danish case in terms of increased tree growth and therefore higher predation rates and decreased visibility. In Iceland, rapid shrub encroachment, which negatively affects waders, is probably both due to warmer temperatures and reduced sheep grazing (Gunnarsson, 2020).

Human management
Anthropogenic factors can be grouped into negative drivers such as draining, agricultural intensification, and fertilizing, and positive drivers like grazing and mowing (Table 1). The negative factors have for centuries changed the dynamic wetlands into areas suitable for modern agriculture. This has affected the key ecological patterns and processes of importance for wader population sustainability. Many earlier studies have identified these changes over Europe (Cronert, 2010;Emanuelsson, 2009;. The most important negative driver is draining. The need for more effectively used arable and forestry land and the change of agricultural methods from the end of the 18th century increased draining (Gadd, 2000;. Overall, this implies a transition from the creation of wader habitat as a side effect of sustaining local livelihoods based on animal husbandry, to active top-down public sector biodiversity conservation which is often disconnected from farmers on the ground. For some farmers, however, experts reported that habitat management has become a main income through subsidies and tourism activities. Another major influence on breeding waders is the timing of mowing grasslands (Schroeder et al., 2012).

Wetland restoration
Restoration of wetlands for wader population sustainability requires a system perspective that encompasses entire landscapes and also includes the social-ecological processes. with a positive effect on the wader population (Ottvall, 2015). The predator species included in the protection shooting are corvids, and badger (Meles meles), fox, marten (Martes martes), and mink (Neovison vison). The conservation focus on single threatened predator species without a systems perspective increases the intensity of predation on adult waders. One example is the introduction of artificial nest boxes for peregrine falcons (Falco peregrinus) and kestrel (Falco tinnunculus) (Svahn, 2016). Successful conservation of red kite (Milvus milvus) is another example Manton et al., 2016).
According to one of the experts, this insight led to canceling the introduction of peregrine falcon nest boxes in one case study.

Recreation
In all three central Swedish case study landscapes, the main recreation activities in the wetlands are birdwatching and fishing. The fishing associations support wetland restoration due to the open water for fish, especially pike (Esox lucius). Fishing possibilities also increase the landowners' interest in wetlands. Wetlands as a green infrastructure close to urban areas are also identified to create social benefits through outdoor activity. For instance, Beery and Jönsson (2015) showed that the Kristianstad Nature Centre plays an important role by providing nature inspiration to its visitors to use and experience the wet grasslands of the Kristianstad Vattenrike Biosphere Reserve.

Wetland restoration
To maintain or restore wader populations, wetland restoration has been attempted in several of the case study landscapes. In Sweden evaluations of restoration projects have found that, from a governance point of view, successful wetland restoration requires knowledge about wetland grassland history , and sustaining multiple synergies (Manton et al., 2016). This includes not only grazing and mowing but also a functional landscape-level habitat network with meadows and open water (Jönsson, 2015).
Pumping of water to modify the water level, which also benefits pike reproduction, and predator control are other good examples (Karlsson, 2017;Ottvall et al., 2008;Wallin et al., 2009). From a systems point of view, the single focus on wetland management may thus be detrimental as the management of the surrounding agricultural landscape is of crucial importance for successful wader conservation. The current homogenisation and afforestation of the wider landscape promoting predator populations is in this respect a challenge (Johannesdottir et al., 2019;Ottvall et al., 2008). Therefore, the tendency to prioritize management efforts only to areas with formal protection is problematic (Bergner, 2013).

| Systems analysis
3.4.1 | Theme 1: Landscape ecology, wader bird breeding success The first CLD model focused on the breeding success of waders ( Figure 4). The predator factors have been combined in one group called "predator intensity" in order to allow the inclusion of both predation of nests, chicks and adults .
A higher number of predators increase both adult predation and nest predation, which impact breeding success. The decision to introduce protective culling, i.e., shooting and trapping predators, is a regional outside management driver (Fletcher et al., 2010). Relatively few loops are identified in the ecological system while many drivers from outside the wet grassland system seem to be important.
The main outside drivers on global and national levels were "nature conservation policy" and "climate change," which according to experts increases vegetation encroachment and thus predation due to increased availability of perches for predators.
On the local scale the drivers "Land management" and "Vegetation encroachment" affect breeding success through "suitable patch size" and "predator intensity." Predation can reduce the effective patch area. For example, within grassland patches, perches on wet grasslands increase predation risk. Conversely, a large patch size with more mobbing birds will reduce predation risk. For example, lapwings actively defend themselves against predators, and therefore other waders tend to breed close to lapwings and have somewhat higher breeding success. The "Land management" driver is further analyzed in the model for farmers' interest in waders, see Figure 5. The driver "grazing" by cattle and population growth of geese (Tuvendal & Elmberg, 2015),.
which regulates the grazing intensity is also linked to local land management (Sabatier et al., 2010).
One reinforcing and two balancing loops are found in the ecological wader system. The term "wader bird arrival" explains the number of waders deciding to the prospect on a certain geographic area. The population loop, R1, indicates that more arriving waders lead to a higher wader density (settlement after initial spring prospecting) and higher breeding success, which positively influence a higher wader bird arrival in subsequent years (increased recruitment). Another internal driver is the water table at the time of arrival. The two balancing loops, B1 and B2, depend on the farmers' decision to mow.
Mowing causes a change in vegetation composition and less vegetation growth due to nutrient output. Both loops result in low vegetation that increases the wader bird arrival.

| Theme 2: Optimal land management for wader birds
The second CLD modeling theme was the dynamics behind farmer's interest in wet grassland management for wader birds ( Figure 5).
Two reinforcing loops, R1, R2, increase the income of the local farmers and their interest in land management positive for wader birds.
The third loop, R3, is the financial incentive loop triggered by an F I G U R E 4 The local ecological system of wader breeding success and population development. Global/national outside drivers are given in italic increased interest of municipality decision-makers in biodiversity conservation and therefore a leverage point to wetland management on a landscape scale. The fourth loop affects the amount of water in the farmers' wells.
The three income loops work together but the time when they become effective can vary. The leverage point in R3 starts the process on a landscape scale. As many of the wet grasslands are already grazed today, the prerequisite for R1, the food loop, exists. Meat production from natural grazed wetland, increases the "Farmer's income" and therefore the "farmer's interest in waders" and a higher local "Food actor co-operation." A higher co-operation not only between farmers, but also with actors in the tourism sector, results in higher meat production through the number of animals grazing the land. More intensive grazing is a factor in the ecological system, decreasing the vegetation height and increasing wader bird arrival, i.e., the willingness of waders to choose a specific wetland. The nature tourism reinforcing loop, R2, says that a higher amount of "Nature tourism" increases the "Farmer's income," the "Farmer's interest in waders," and the "Land management for wader birds." Increased "Land management" can increase "Nature tourism" either through wetland management for fishing tourism, R2a, or higher water quality through increased grass mowing and less nutrient in the soil, R2b.
Land management suitable for waders also increases the number of bird watchers. A potential grazed land with high biodiversity starts the financial incentive loop, R3, which includes the following relationships: more "Income incentives" increases the "Farmer's interest in waders" and gives a higher amount of "Nature tourism" leading to a higher "Village survival," which increases the "Community interest" for "Biological conservation" (for wetlands) resulting in more "Financial incentives" from the municipality.

| Theme 3: Society's interest in wetlands
Two external drivers on the national level start the running of the loops through "Community interest in wetlands." Community includes public sector decision-makers in society. Additional objectives include the need for climate change mitigation using the wetland as a CO 2 sink and the environmental policy to keep and increase biodiversity. The variable "Community interest wetlands" is also included in the R3 loop in Figure 6. In the community interest system, there are three reinforcing loops and two balancing loops.
All the reinforcing loops go through the "Community interest in wetlands." The income loop, R1, starts when the community develops a higher interest in establishing wet grasslands forced by the external drivers. The greening of the area results in more "Settlement of F I G U R E 5 The management system of wet grasslands for wader birds. How to increase the farmer's interest green quality" and a higher "Tax income" increasing the "Community interest in wetlands." There may be a multi-year lag between establishment of wetlands and the settlement of green quality.
The loop access to land for recreation, R2, starts as soon as a higher "Community interest in wetlands" gives more "Establishment of wetlands," which gives a higher "Access to land" for tourists and citizens which results in a higher "Community interest in wetlands." The Inspiration loop, R3, focus on that a higher "Establishment of wetlands" -gives a higher "wader bird population" through land management and therefore a higher amount of "Media reporting," which gives more "Inspiration" to the community politicians and a higher "Community interest" in wetlands. This loop has a delay as it takes time to increase the wader population after the establishment of suitable wetlands.
This system also has two balancing loops. The first, B1, tells us that "More green settlements" gives a higher "Need for recreation" and a higher amount of "Recreation activity." More recreation activity results in less "Citizen stress" and less "Need for recreation." The other balancing loop, B2, the property price loop, hampers the amounts of citizen moving into the area due to the increasing cost of housing.
The ecological system in Figure 4 is linked together with the social system in Figures 5 and 6  driver, climate change, will affect both the ecological system, as described in Figure 4, and the community interest system (Figure 6).

| Validation in space and time
For validation of the systems analysis in the current study, we chose to discuss the results in the contexts of two landscapes characterized by a historical focus on animal husbandry and the establishment and maintenance of grasslands with different levels of wet grassland conservation success. These were Kristianstad Vattenrike in southern Sweden, which has been unsuccessful in terms of conserving wader populations (see Manton et al., 2016), and Friesland in the Netherlands, which has been effective at the local level (Kentie, 2015). For details, see Appendix S2.

Using historical maps and agricultural statistics of Kristianstad
Vattenrike, Manton and Angelstam (2018)  and more productive grass species (Harms et al., 1987). To cope with this, conservation of meadow birds is attempted by avoiding disturbance, not using fast-growing grass species, increasing water table, leaving grass uncut around nests, and putting a metal frame over it.
However, according to Montfoort (2020) targets for Friesland are unlikely to be achieved without substantial changes in supportive systems for farmers to participate in nature conservation and restoration measures. To conclude, as in the case study wetlands used for systems analysis (Figure 6), the social system dimensions are neglected in Friesland.

| Systems analysis as tool for knowledge production and learning
As there are numerous factors that, simultaneously but with varying time lags, may affect the functionality of green infrastructures the frequent lack of systems perspective in biodiversity conservation policy is problematic (Harvey et al., 2017). Viewing a wet grassland landscape as a social-ecological system highlights the complex interactions among multiple factors and the dynamic and nonlinear characteristics of processes involved. Systems analyses of landscapes as social-ecological systems can support collaborative learning in individual wet grassland landscape by diagnosing the state and trends of land cover types as green infrastructures, and setting priorities for conservation, management, and restoration.
Successful management of ecological systems includes rewetting, mowing, and grazing by cattle and horses in sufficiently large patches of wet grasslands, and predator control (McMahon et al., 2020). This is confirmed in several wetland landscapes other than the ones we analyzed (Kuresso & Mägi, 2004). In Estonia, Rannap et al. (2017) found that extensive grazing and no woody vegetation were positive for wader breeding conditions. Located in the East-Atlantic flyway for migrating birds the Matsalu National Park is situated around a river delta and the coastal grasslands are maintained using a combination of low-intensity grazing and mowing regimes to create an open sward. The Dviete floodplain in southeastern Latvia on the left bank of the Daugava River was managed by mowing and grazing until the mid-20th century (Gruberts & Štrausa, 2011). During the Soviet period, collective farming was introduced with mechanized cultivation of grasslands on drier soil, and wet meadows were abandoned. Conservation management projects have restored open grassland by clearing vegetation and introducing cattle and Konik horses, and restoring 2 km of natural river meanders (Ķerus et al., 2015).
Predation on nests and chicks is an example of links between the dynamics of ecological and social systems (Laidlaw et al., 2021;. Comparing five of the wet grassland landscapes in this study Manton et al. (2019) found that corvid bird abundance, and availability of their resources, increased with increasing agricultural land-use intensity. This is consistent with the increase in abundance of the corvid species in southern Sweden over the past few decades (Ottvall et al., 2009), especially in a mixed mosaic landscape of agriculture and forest (Andrén, 1992). Also, the abundance of raptors has changed. In their analysis of raptor observations at the Danish Tipperne wet grassland case study 1930-2011, Meltofte and Amstrup (2013 conclude that almost all raptor species have increased due to multiple drivers. First, persecution of raptors decreased considerably until they gained full protection in 1967. Second, environmental pollutants peaked in the 1960s and 1970s, but later, raptor populations gradually recovered. For example, Thorup and Bregnballe (2015) showed that the presence of peregrine falcons (Falco peregrinus) at Tipperne in the wader breeding season is very much more frequent in the past 15-20 years than observed in any previous periods. Third, emergence of conifer plantations during the 20th century likely improved the conditions for sparrowhawk (Accipiter nisus), goshawk (Accipiter gentilis), common buzzard (Buteo buteo), and kestrel (Falco tinnunculus). Fourth, meadow management has changed. Initially, meadows were intensively used for mowing and grazing, which are negative factors for important predatorprey species such as water vole (Arvicola terrestris) and field vole (Microtus agrestis). Controlling predators can thus be effective.
Beginning in 2008 culling and trapping of mammalian (fox, badger) and avian (corvids and gulls) predators was carried out in the Swedish Öland wet meadow landscape (Karlsson, 2017;Ottvall, 2015). Early spring culling was most effective to increase chick survival of black godwits. Corvids had only a minor impact on nest predation (Ottvall et al., 2009). The role of predators has been highlighted also in other systems. Regarding recent declines in Norwegian seabird populations, Fauchald et al. (2015) concluded that apart from ecosystem changes affecting the availability of prey, increased predation is from avian and mammalian predators is a key factor. Especially for declining and threatened populations, this stressor is particularly important to control. Thus, increased predation on seabirds is an unintended consequence of the recovery of sea eagle Haliaeetus spp. populations (Hipfner et al., 2012).
In a natural experiment, Hentati-Sundberg et al. (2021) confirmed this and also reported a previously concealed guarding effect by tourist groups on an iconic seabird colony in the Baltic Sea.
Triggered by the COVID pandemic, a halt of visiting tourists in 2020 led to a strong increase in presence of white-tailed eagles but facilitated egg predation from herring gulls (Larus argentatus) and hooded crows (Corvus cornix). Thus, a social-ecological systems perspective is crucial for successful seabird management.
The main leverage point in the social systems is the farmer's interest in wetland management which is triggered by financial income loops. In the absence of livelihoods based on grasslands as a driver to maintain suitable land covers for waders, adequate, longterm economical subsidies form the basis for wetland establishment and grassland maintenance (Gren et al., 2021;Hansson et al., 2012).
However, an unfavorable social-ecological driver that these areas do not provide is a long-term steady income based on production, but income is dependent on short-term subsidy programs for restoration (Borgström et al., 2016). As the governmental subsidy system is complex, not transparent, and short-term, the identified local income reinforcing loops are fundamental for grassland management.
The loop including meat production (R1, Figure 5) is in line with the growing interest for high-quality meat from grazed semi-natural grasslands (Emanuelsson, 2009). To secure a long-term economic stability for maintenance, Gren et al. (2021) even suggested a climate tax on food consumption with refunding to farmers for ecosystem services. Outdoor recreation and nature-based tourism are other sources of income (Margaryan & Fredman, 2017). Wet grassland restoration in urban settings has led to increasing housing prices and the increased green infrastructure to a perception of better human health and well-being (Stoltz, 2020).
Complex social-ecological problems such as maintenance of green infrastructure are frequently handled from a top-down silo perspective with attendant poor coordination between different government agencies and often conflicting advice or decisions further reduce legitimacy at the local society level (Schlyter et al., 2013). National nature and landscape conservation policy tend to lack a systems perspective (Borgström et al., 2016). This applies not only to the ecological landscape dynamic, which is demonstrated by the initiative to put up predator nest boxes close to wader wetlands (Thorup & Bregnballe, 2015) but mainly by not recognizing the social and livelihood aspects of farming and grassland management (Raatikainen & Barron, 2017). This is especially evident with regard to subsidies for wetland establishment and management in Sweden.
New modes of governance to satisfy complex environmental objectives on EU, national and local levels identified deliberative methods and dialog as important for a positive outcome (Bäckstrand et al., 2010). Wetland projects with a positive result for nutrient retention and biodiversity development are often landowner driven, where the transformation of practical knowledge and adaptive learning is a prerequisite for effective measures (Hansson et al., 2012). However, in contrast, authorities often devise top-down administrative processes, seen as safer for reaching environmental objectives as opposed to bottom-up stakeholder-based approaches. For instance, Birge et al. (2017) found that in Finland, administrative officials were opposed to a suggested result-oriented payment scheme for grasslands, owing to their perceptions that this approach does not fit into the current institutionalized program.
In the future, global warming will increase temperature and change the precipitation pattern, thus affecting the local ecosystems' water and vegetation drivers but also social drivers as the local community's awareness of changes in the landscape and the need for mitigation. The identification of wetlands as possible CO 2 sinks , and flood mitigation (Barbedo et al., 2014) call for long-term management through extensive low intensive grazing (Benstead et al., 1997), which is only possible with a continuous income from farming and tourism or environmental subsidies. The driver to establish more wetlands for waders at the community level is connected to biodiversity conservation, a growing social interest in settlements with "green" qualities and landscape recreation, and climate change.

| Placing landscape case studies in the systems analyses
The eight different case study landscapes which formed the empirical base for the systems analysis face a wide range of challenges and opportunities for sustaining wet grasslands as a green infrastructure for biodiversity conservation and human well-being. Additionally, the histories of two wet grassland landscapes were used for validation. Representing a long gradient from favorable to unfavorable social-ecological conditions for wader bird populations (Figure 3), below we link the systems analysis to these 8 wet grassland landscapes (   during the past two centuries. Bird surveys made in this part of Sweden in the 1930s show that currently extirpated wader bird species like ruff and dunlin were previous regular breeders (Jönsson et al., 2021). Today, the remaining grassland patches are small, the quality is declining, and generalist predators are abundant. Nevertheless, this area has repeatedly been presented as a success story of environmental governance and adaptive co-management of green infrastructure (Millennium Ecosystem Assessment, 2005;Schultz et al., 2015). In spite of this, restoration efforts have been short-lived and the conservation status of the priority green infrastructure being semi-natural grassland ecosystems with an unfavorable situation for wader birds has remained (Cronert, 2010(Cronert, , 2014 Manton et al., 2016Manton et al., , 2019. On the other hand, today, the role of these wet grassland areas for recreation and nature-based tourism has become increasingly important . This is in clear contrast with the past when wet grasslands were an important resource for local and regional livelihoods linked to animal husbandry.  (Beery & Jönsson, 2015, 2017, the wader birds have not (Manton et al., 2016). Coordination and integration of social system actors is often a limiting factor for successful wader bird conservation (Montfoort, 2020), and not lack of ecological knowledge.

| Multiple landscape case studies as a tool
Implementing policy on green infrastructure requires evidencebased knowledge about the states and trends in terms of TA B L E 2 Overview of barriers (−) and bridges (+) for wader bird conservation in eight wet grassland landscape case studies biodiversity conservation and provisioning of ecosystem services, which is combined with cross-sectoral multi-level environmental governance. This implies a social-ecological systems approach (Herzon et al., 2021). Maintaining wet grasslands as a green infrastructure is more than just about managing land covers and needs to involve many factors at multiple spatial scales. A functional green infrastructure is not only about patch quality linked to hydrology, grazing, and mowing; patch size; and functional connectivity of acceptable patches . It is also trophic interactions such as predation (McMahon et al., 2020), for example on nests and chicks by corvid birds .
The values of wet grasslands are co-generated by interacting social and ecological systems and linked to traditional land-use practices aimed at producing food and feed. To replace these disappearing practices agro-environmental schemes have been developed with the aim to maintain biocultural values as the "key products." This has indeed provided support for grassland landscapes as sites for outdoor recreation (Beery & Jönsson, 2015), which is much less complicated than to secure functional green infrastructure for biodiversity conservation. Thus, land management and governance should be developed with a better awareness of the challenges linked to different benefits provided by wet grassland landscapes as social-ecological systems. The implementation of specific policy instruments to financially support land managers to supply values to society represents a future challenge that both research and policy makers should focus upon (de Groot et al., 2010). Second, both anthropogenic and natural processes from individual land cover patches through to landscape and regions need to be understood.
Hence, the conservation of semi-natural grasslands as functional green infrastructure is complex (Benstead et al., 1997) and requires continuous knowledge production and learning, and ongoing maintenance and monitoring programs to assess consequences on the ground (Rauschmayer et al., 2009). The systems analysis approach to enhance collaborative learning among researchers and stakeholders through analyses of multiple landscape case studies is an appropriate tool for practicing transdisciplinary research through collaboration among natural and social scientists and practitioners in different contexts.
Increasing demands for natural resources, an exodus from rural regions, biodiversity conservation, and climate change require environmental governance systems that can exercise transformative change towards sustainable landscapes. This requires evaluation of policy implementation in terms of what develops between the establishment of an agreed policy and the ultimate impact of subsequent actions in the real world (Rauschmayer et al., 2009). Three key evaluation steps are (1) the policy process (e.g., who takes part?), (2) outputs (e.g., policy instruments, planning processes?), and (3) the consequences in terms of outcomes on the ground (e.g., the functionality of ecological networks, or green infrastructures, forming trust, livelihood for landowners, supporting human well-being and biodiversity conservation). Given that evaluation methods need to recognize that restoration is driven by multiple rationales (Baker & Eckerberg, 2016) the outcomes on the ground take a long time to develop, an alternative is comparative macroecological comparative studies based on multiple place-and area-based case studies representing different trajectories of land use and land cover change and social-ecological systems can be seen as "landscape experiments" is another alternative.

ACK N OWLED G EM ENTS
This study was supported by grants from "Marcus and Amalia Wallenbergs Minnesfond" and FORMAS [grant numbers 2011-1737 and 2017:1342] to Per Angelstam. We thank Eelke Folmer and three anonymous reviewers for careful and constructive comments on the manuscript.

CO N FLI C T O F I NTE R E S T
None of the co-authors have any conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data are available in